CN111495970A - A rolling method for reducing surface cracking of TC4 titanium alloy smelted in EB furnace - Google Patents

Abstract

The invention discloses a rolling method for reducing surface cracking of TC4 titanium alloy smelted in an EB furnace, and belongs to the field of plastic forming. The present invention directly rolls the TC4 titanium alloy as-cast slab into a high-quality plate by the method of combining direct rolling and recrystallization annealing heat. On the one hand, the production process of the TC4 titanium alloy is shortened, the processing cost is reduced, and the other is On the one hand, the edge cracking and center surface cracking during the titanium alloy rolling process are reduced, the surface quality of the finished sheet is good, and a high-quality TC4 titanium alloy sheet is finally obtained.

Description

A rolling method for reducing surface cracking of TC4 titanium alloy smelted in EB furnace

technical field

The invention belongs to the field of plastic forming, and particularly relates to a rolling method for reducing surface cracking of TC4 titanium alloy smelted in an EB furnace.

Background technique

TC4 titanium alloy is a typical (α+β) two-phase titanium alloy, which has the characteristics of high strength, good corrosion resistance, excellent welding performance, etc. It has a wide range of applications in aerospace and other fields, but TC4 titanium alloy The cold-rolled forming of the alloy is difficult and prone to surface cracking, and the production cost is too high, which limits the application of TC4 titanium alloy.

The main process of domestic titanium TC4 alloy sheet production is that the as-cast billet is forged for several times, and then rolled into a sheet by two-roll pass rolling, stepping rolling, roll skew rolling, and Y-rolling. The production process is long, and the slab is forged and blanked, resulting in low production efficiency and high cost of titanium alloy sheets.

TC4 titanium alloy as-cast billet will have defects such as loose structure, which leads to a large gap between the quality and mechanical properties of the rolled sheet and the sheet rolled from the dense forging billet, which cannot meet the requirements of the national standard and the needs of use in various fields. At the same time, if the heating temperature and rolling process of TC4 titanium alloy are not controlled accurately during the rolling process, the stress distribution will be uneven during the rolling process, and the edge cracks and deep surface cracks will easily occur in the plate after rolling.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the prior art, the object of the present invention is to provide a rolling method for reducing the surface cracking of the TC4 titanium alloy smelted in the EB furnace. The TC4 titanium alloy prepared by the present invention has low cost and high quality, and can overcome the Phenomenon of edge and surface cracks during rolling of TC4 titanium alloy.

The technical scheme adopted in the present invention is as follows:

A rolling method for reducing surface cracking of TC4 titanium alloy smelted in EB furnace, comprising the following steps:

Step (1), heating the TC4 titanium alloy ingot to a temperature of 5-25°C below the phase transition temperature, and keeping the temperature for 30-60min;

In step (2), one-fire rolling is performed on the ingot perpendicular to the grain growth direction, and the deformation amount of each pass is 16% to 21%, and the cumulative deformation amount of one fire is 61% to 65%. The original grains are completely broken to obtain the first rolled billet;

In step (3), the first rolling billet is heated to 940-970° C., kept for 30-60 minutes, and then rolled in the second fire, the rolling direction is perpendicular to the rolling direction of the first fire, and the deformation amount per pass is 16%～ 26%, the cumulative deformation of the second fire is 61% to 70%, and the second rolling billet is obtained;

In step (4), the second rolling billet is heated to 910-940° C., kept for 30-60 minutes, and then rolled in the third fire. The rolling direction is consistent with the rolling direction of the second fire. 26%, the cumulative deformation of the three fires is 61% to 70%, and the final rolling TC4 titanium alloy sheet is obtained;

In step (5), the final rolling TC4 titanium alloy sheet is subjected to recrystallization annealing treatment, and air-cooled to obtain the final finished TC4 titanium alloy sheet.

Preferably, in the step (2), the rolling speed is 0.5-1.1 m/s, and the cumulative deformation amount in one fire is 61%-65%.

Preferably, in the step (3), the rolling speed is 0.5-1.1 m/s and the cumulative total deformation is 84.5%-89%.

Preferably, in the step (4), the rolling speed is 0.5-1.1 m/s and the cumulative total deformation is 94%-97%.

Preferably, in the step (5), the annealing temperature is 780°C to 840°C, the holding time is 60 to 90 minutes, and air cooling is performed.

Compared with the prior art, the beneficial effects of the present invention are:

In the present invention, the rolling method for reducing the surface cracking of TC4 titanium alloy smelted in EB furnace adopts electron beam cooling bed smelting TC4 titanium alloy slab as material, and the billet rolling of the present invention is carried out in the range of 5 to 25° C. below the phase transition temperature. Rolled, directly rolled into sheet. In the two-phase region, it is directly rolled into a sheet, and the deformation resistance of the material is small during the rolling process. At the same time, the blanking and forging process of TC4 titanium alloy by vacuum consumable arc melting is omitted, which shortens the process flow and reduces the cost of TC4 titanium alloy. The invention avoids the phenomenon of surface cracks and edge cracks caused by uneven stress distribution during the hot rolling of TC4 titanium alloy by reciprocating multi-pass rolling in each fire, and improves the rolling yield. The invention solves the problems of edge cracks and center cracks after the titanium alloy plate is rolled by the method of forging-free direct rolling, through three-fire large deformation rolling, and after recrystallization annealing treatment, and the plate obtained by the present invention has an equiaxed microstructure. The distribution is uniform, the equiaxed α phase is small, the surface quality is good, and the performance meets the requirements of the national standard.

Further, the rolling speed is 0.5-1.1 m/s, and the use of a smaller deformation rate can further effectively prevent edge cracking, longitudinal and transverse cracks from increasing deformation resistance during the rolling process.

Further, the recrystallization annealing temperature is 780°C to 840°C, the holding time is 60 to 90 minutes, and air cooling is performed. The higher the annealing temperature, the greater the recrystallization rate, and the finer the grains after recrystallization annealing. Recrystallization annealing at the recrystallization temperature in this process is beneficial to the formation of equiaxed α-structure after rolling deformation in the two-phase region, and at the same time prevents the grains from growing again.

Description of drawings

Fig. 1 is the process flow schematic diagram of the present invention.

2 is a SEM photo of the microstructure of a TC4 titanium alloy sheet obtained by forging-free direct rolling in Example 1 of the present invention.

3 is a SEM photo of the microstructure of a TC4 titanium alloy sheet obtained by forging-free direct rolling in Example 2 of the present invention.

4 is a SEM photo of the microstructure of a TC4 titanium alloy sheet obtained by forging-free direct rolling in Example 3 of the present invention.

5 is a SEM photo of the microstructure of a TC4 titanium alloy sheet obtained by forging-free direct rolling in Example 4 of the present invention.

Detailed ways

In order to make those skilled in the art understand the technical solutions of the present invention more clearly, the examples given below are to illustrate the present invention in detail. It should be pointed out that the following examples are only suitable for further explanation of the present invention. Obviously, the described embodiments are only a part of the present invention, and should not be construed as limiting the protection scope of the present invention.

1, the present invention reduces the rolling method of EB furnace smelting TC4 titanium alloy surface cracking, comprising the following steps:

Step (1), heating the TC4 titanium alloy as-cast slab to a temperature of 5-25°C below the phase transition temperature, and keeping the temperature for 30-60min;

Step (2), using an 8-roll hot rolling mill to perform one-fire rolling along the direction perpendicular to the grain growth, the deformation amount of each pass is 16% to 21%, and the cumulative deformation amount of one fire is 61% to 65%;

In step (3), the billet obtained in step (2) is heated to 940-970° C., kept for 30-60 minutes, and then rolled in the second fire, the rolling direction is perpendicular to the rolling direction of the first fire, and the deformation amount per pass is 16% ～26%, the cumulative deformation of the second fire is 61%～70%;

In step (4), the billet obtained in step (3) is heated to 910-940° C., kept for 30-60 minutes, and then rolled in the third fire. The rolling direction is consistent with the rolling direction of the second fire, and the deformation amount per pass is 16%. ～26%, the cumulative deformation of the three fires is 61%～70%;

In step (5), the final rolled TC4 titanium alloy plate is subjected to recrystallization annealing heat treatment and air-cooled to obtain the final finished TC4 titanium alloy plate.

Among them, the TC4 titanium alloy as-cast slab is obtained by electron beam cooling bed melting (EBCHM). In step (2), the rolling speed is 0.5-1.1 m/s, and the accumulated deformation amount in one fire is 61%-65%. In step (3), the cumulative deformation amount of the second fire is 61%-70%, and the cumulative total deformation amount is 84.5%-89%. In step (4), the cumulative deformation amount of the three fires is 61%-70%, and the cumulative total deformation amount is 94%-97%. In step (5), the annealing temperature is 780° C. to 840° C., the temperature is kept for 60 to 90 minutes, and air-cooled.

The invention adopts electron beam cooling bed to smelt TC4 titanium alloy flat ingot as the material, the billet rolling is in the range of 5-25°C below the phase transition temperature, the rolling speed is 0.5-1.1m/s, and the reciprocating direction is perpendicular to the grain growth direction. Rolling is carried out for 4 to 6 passes, the deformation of each pass is 16% to 21%, and the cumulative deformation of billet rolling is 61% to 65%. After the billet is rolled in the near β region, it is directly rolled into a sheet in the two-phase region, and the deformation resistance of the material during the rolling process is small. The technological process reduces the cost of TC4 titanium alloy. Large deformation rolling is used in the three-pass rolling process, and the cumulative total deformation of the three-pass rolling is 94% to 97%. By matching the heating temperature, rolling rate, rolling pass and deformation amount, the phenomenon of surface cracking and edge cracking caused by uneven temperature distribution and uneven stress distribution during hot rolling of TC4 titanium alloy can be avoided, and the rolling process can be improved. yield. In the invention, by controlling the rolling parameters to match, the billet rolling is carried out reciprocatingly along the direction perpendicular to the grain growth, and the grain crushing effect is good. After the three-fire large deformation rolling and recrystallization annealing treatment, the edge cracks and center cracks of the titanium alloy sheet after rolling are reduced, and the surface quality of the finished sheet is improved. After rolling, the equiaxed structure is uniformly distributed, and the equiaxed α phase is fine , the performance meets the requirements of the national standard.

Example 1

The rolling method for reducing the surface cracking of TC4 titanium alloy smelted in the EB furnace in the present embodiment, the rolling process is shown in Figure 1, and the specific steps are as follows:

(1) the TC4 titanium alloy of the present embodiment 1, adopts the continuous temperature rise method to measure this alloy phase transition temperature to be 995 ℃;

(2) The TC4 titanium alloy slab ingot is sent to the heating furnace and heated to 990 ℃ with the furnace, and kept for 50min;

(3) rolling the TC4 titanium alloy slab heated in step (2) by one-fire rolling at a rolling speed of 1.1 m/s, reciprocating rolling along the direction perpendicular to the grain growth, with a deformation amount of 16% per pass , the rolling passes are 6 times, and the cumulative deformation is 65%;

(4) the billet rolled in step (3) is sent to the heating furnace and heated to 970 ℃ with the furnace, and kept for 50min;

(5) The billet heated in step (4) is subjected to two-fire rolling, the rolling speed is 1.1 m/s, and the rolling is reciprocated along the direction perpendicular to the first-fire rolling direction, and the deformation amount of each pass is 16%. 6 passes, the total deformation of the second fire is 65%, and the cumulative deformation is 88%;

(6) the billet rolled in step (5) is sent to the heating furnace and heated to 940 ℃ with the furnace, and kept for 50min;

(7) The billet heated in step (6) is subjected to three-fire rolling, the rolling speed is 1.1 m/s, and rolling is carried out along the second-fire rolling direction, and the deformation amount of each pass is 16%. 6 times, the total deformation of the three fires is 65%, and the cumulative deformation is 96%;

(8) The alloy sheet obtained after rolling in step (7) is sent to a heating furnace for recrystallization annealing. The annealing temperature is 840° C., the holding time is 90 minutes, and the air cooling is performed. Through recrystallization annealing, the degree of equiaxing of the microstructure is increased.

The TC4 titanium alloy sheet prepared in this example is rolled for three times, and the total deformation is 96%. The obtained alloy has good comprehensive mechanical properties, and has no edge cracks and surface cracks during the rolling process. The surface quality is good. Tensile samples were taken from the rolled product sheet, and the mechanical properties were measured as shown in Table 1. The microstructure was shown in Figure 2. The microstructure was composed of equiaxed α structure and lamellar α structure, and the equiaxed structure was distributed. Uniform, equiaxed alpha phase size of about 12 μm.

Table 1

Example 2

The rolling method for reducing the surface cracking of TC4 titanium alloy smelted in the EB furnace in the present embodiment, the rolling process is shown in Figure 1, and the specific steps are as follows:

(1) the TC4 titanium alloy of the present embodiment 2, adopts the continuous temperature rise method to measure this alloy phase transition temperature to be 995 ℃;

(2) The TC4 titanium alloy slab ingot is sent to the heating furnace and heated to 980 ℃ with the furnace, and kept for 40min;

(3) rolling the TC4 titanium alloy slab heated in step (2) by one-fire rolling at a rolling speed of 0.8 m/s, reciprocating rolling along the direction perpendicular to the grain growth direction, and the amount of deformation per pass is 21% , the rolling passes are 4 times, and the cumulative deformation is 61%;

(4) the billet rolled in step (3) is sent to the heating furnace and heated to 955 ℃ with the furnace, and kept for 40min;

(5) The billet heated in step (4) is subjected to two-fire rolling, the rolling speed is 0.8m/s, and the rolling is reciprocated along the direction perpendicular to the first-fire rolling, and the deformation amount of each pass is 26%. 4 passes, the total deformation of the second fire is 70%, and the cumulative deformation is 88%;

(6) the billet rolled in step (5) is sent to the heating furnace and heated to 925 ℃ with the furnace, and kept for 40min;

(7) The billet heated in step (6) is subjected to three-fire rolling, the rolling speed is 0.8 m/s, and rolling is performed reciprocatingly along the second-fire rolling direction, and the deformation amount of each pass is 26%. 4 times, the total deformation of the three fires is 70%, and the cumulative deformation is 96%;

(8) The alloy sheet obtained after rolling in step (7) is sent to a heating furnace for recrystallization annealing, the annealing temperature is 810° C., the holding time is 70 minutes, and the equiaxed crystal is formed by air cooling.

The TC4 titanium alloy sheet prepared in this example is rolled for three times, and the total deformation is 96%. The obtained alloy has good comprehensive mechanical properties, no edge cracking and surface cracks during rolling, and the surface quality is good. Tensile specimens were taken from the rolled finished sheet, and the mechanical properties were measured as shown in Table 2. The microstructure was shown in Figure 3. It can be seen from Figure 3 that after recrystallization and annealing of the finished sheet, the structure was composed of equiaxed α phase. It is composed of a small amount of short rod-shaped α tissue, the distribution of equiaxed tissue is uniform, and the size of the equiaxed α phase is about 7 μm.

Table 2

Example 3

The rolling method for reducing the surface cracking of TC4 titanium alloy smelted in the EB furnace in the present embodiment, the rolling process is shown in Figure 1, and the specific steps are as follows:

(1) the TC4 titanium alloy of the present embodiment 3, adopts the continuous temperature rise method to measure the phase transition temperature of this alloy and is 995 ℃;

(2) The TC4 titanium alloy slab ingot is sent to the heating furnace to be heated to 970 ℃ with the furnace, and kept for 60min;

(3) rolling the TC4 titanium alloy slab heated in step (2) by one fire, the rolling speed is 0.5m/s, and rolling back and forth perpendicular to the grain growth direction, and the deformation amount per pass is 16% , the rolling passes are 6 times, and the cumulative deformation is 65%;

(4) the billet rolled in step (3) is sent to the heating furnace and heated to 940 ℃ with the furnace, and kept for 60min;

(5) The billet heated in step (4) is subjected to two-fire rolling, the rolling speed is 0.5 m/s, and the rolling is reciprocated along the direction perpendicular to the first-fire rolling, and the deformation amount of each pass is 26%. 4 passes, the total deformation of the second fire is 70%, and the cumulative deformation is 89%;

(6) the billet rolled in step (5) is sent to the heating furnace to be heated to 910 ℃ with the furnace, and kept for 60min;

(7) The billet heated in step (6) is rolled in three fires, the rolling speed is 0.5m/s, and the rolling is reciprocated along the rolling direction of the second fire. The deformation amount of each pass is 26%, and the rolling pass 4 times, the total deformation of the three fires is 70%, and the cumulative deformation is 97%;

(8) The alloy sheet obtained after rolling in step (7) is sent to a heating furnace for recrystallization annealing, the annealing temperature is 840° C., the holding time is 60 minutes, and air cooling is performed to promote the formation of equiaxed crystals through recrystallization annealing.

The TC4 titanium alloy sheet prepared in this example is rolled for three times, and the total deformation is 97%. The obtained alloy has good comprehensive mechanical properties, and there is no edge cracking and surface cracking during the rolling process. Tensile specimens were taken from the rolled product sheet, and the mechanical properties were measured as shown in Table 3. The microstructure was shown in Figure 4. There was almost no lamellar α structure in the microstructure, and the equiaxed structure was evenly distributed, etc. The size of the axial α phase is about 11 μm, indicating that the degree of equiaxing of the plate after recrystallization annealing is better.

table 3

Example 4

The rolling method for reducing the surface cracking of TC4 titanium alloy smelted in the EB furnace in the present embodiment, the rolling process is shown in Figure 1, and the specific steps are as follows:

(1) the TC4 titanium alloy of the present embodiment 4, adopts the continuous temperature rise method to measure this alloy phase transition temperature and is 995 ℃;

(2) The TC4 titanium alloy slab ingot is sent to the heating furnace and heated to 980 ℃ with the furnace, and kept for 40min;

(3) rolling the TC4 titanium alloy slab heated in step (2) by one-fire rolling at a rolling speed of 1.0 m/s, reciprocating rolling along the direction perpendicular to the grain growth direction, and the amount of deformation per pass is 17% , the rolling passes are 5 times, and the cumulative deformation is 61%;

(4) the billet rolled in step (3) is sent to the heating furnace and heated to 955 ℃ with the furnace, and kept for 40min;

(5) The billet heated in step (4) is subjected to two-fire rolling, the rolling speed is 1.0 m/s, and the rolling is reciprocated along the direction perpendicular to the first-fire rolling direction, and the deformation amount of each pass is 21%. 4 passes, the total deformation of the second fire is 61%, and the cumulative deformation is 84.5%;

(6) the billet rolled in step (5) is sent to the heating furnace and heated to 925 ℃ with the furnace, and kept for 40min;

(7) The billet heated in step (6) is subjected to three-fire rolling, the rolling speed is 1.0 m/s, and rolling is performed reciprocatingly along the second-fire rolling direction, and the deformation amount of each pass is 21%. 4 times, the total deformation of the three fires is 61%, and the cumulative deformation is 94%;

(8) The alloy sheet obtained after rolling in step (7) is sent to a heating furnace for recrystallization annealing, the annealing temperature is 800° C., the holding time is 80 minutes, and the equiaxed crystal is formed by air cooling.

The TC4 titanium alloy sheet prepared in this example has been rolled for three times, and the total deformation is 94%. The obtained alloy has good comprehensive mechanical properties, no edge cracking and surface cracks during rolling, and the surface quality is good. Tensile specimens were taken from the rolled finished sheet, and the measured mechanical properties were shown in Table 4. The microstructure was shown in Figure 5. It can be seen from Figure 5 that after recrystallization and annealing of the finished sheet, except for the equiaxed α phase , the tissue has a small amount of short rod-shaped α tissue, the distribution of equiaxed tissue is uniform, and the size of the equiaxed α phase is about 10 μm.

Table 4

Claims (5)

1. a rolling method that reduces EB furnace smelting TC4 titanium alloy surface cracking, is characterized in that, comprises the steps: Step (1), heating the TC4 titanium alloy ingot to a temperature of 5-25°C below the phase transition temperature, and keeping the temperature for 30-60min; In step (2), one-fire rolling is performed on the ingot along the direction perpendicular to the grain growth, and the deformation amount of each pass is 16% to 21%, and the cumulative deformation amount of one fire is 61% to 65%, so as to obtain the first rolling process. billet; In step (3), the first rolling billet is heated to 940-970° C., kept for 30-60 minutes, and then rolled in the second fire, the rolling direction is perpendicular to the rolling direction of the first fire, and the deformation amount per pass is 16%～ 26%, the cumulative deformation of the second fire is 61% to 70%, and the second rolling billet is obtained; In step (4), the second rolling billet is heated to 910-940° C., kept for 30-60 minutes, and then rolled in the third fire. The rolling direction is consistent with the rolling direction of the second fire. 26%, the cumulative deformation of the three fires is 61% to 70%, and the final rolling TC4 titanium alloy sheet is obtained; In step (5), the final rolling TC4 titanium alloy plate is subjected to recrystallization annealing treatment, and air-cooled to obtain the final finished TC4 titanium alloy plate. 2 . A rolling method for reducing surface cracking of TC4 titanium alloy smelted in an EB furnace according to claim 1 , wherein, in the step (2), the rolling speed is 0.5-1.1 m/s. 3 . 3. A rolling method for reducing surface cracking of TC4 titanium alloy smelted in EB furnace according to claim 1, characterized in that, in the step (3), the rolling speed is 0.5-1.1 m/s, and the cumulative total The amount of deformation is 84.5% to 89%. 4. A rolling method for reducing surface cracking of TC4 titanium alloy smelted in EB furnace according to claim 1, characterized in that, in the step (4), the rolling speed is 0.5-1.1 m/s, and the cumulative total The amount of deformation is 94% to 97%. 5. a kind of rolling method for reducing surface cracking of TC4 titanium alloy smelted in EB furnace according to claim 1, is characterized in that, in described step (5), recrystallization annealing temperature is 780 ℃～840 ℃, holding time 60～90min, air cooling.

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